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Abstract:

Body tissue ablation is carried out by inserting a probe into a body of a
living subject, urging the probe into contact with a tissue in the body,
generating energy at a power output level, and transmitting the generated
energy into the tissue via the probe. While transmitting the generated
energy the ablation is further carried out by determining a measured
temperature of the tissue and a measured power level of the transmitted
energy, and controlling the power output level responsively to a function
of the measured temperature and the measured power level. Related
apparatus for carrying out the ablation is also described.

Claims:

1. A method of body tissue ablation, comprising the steps of: inserting a
probe into a body of a living subject; urging the probe into contact with
a tissue in the body; generating energy at a power output level;
transmitting the generated energy into the tissue via the probe; while
transmitting the generated energy determining a measured temperature of
the tissue and a measured power level of the transmitted energy; and
controlling the power output level responsively to a function of the
measured temperature and the measured power level.

2. The method according to claim 1, wherein the generated energy is
radiofrequency energy.

3. The method according to claim 1, wherein the generated energy is
ultrasound energy.

4. The method according to claim 1, wherein the generated energy is
laser-produced light energy.

5. The method according to claim 1, wherein determining a measured
temperature is performed using magnetic resonance imaging analysis.

6. The method according to claim 1, wherein the measured temperature is
an electrode temperature.

7. The method according to claim 1, wherein determining a measured
temperature is performed using ultrasound imaging analysis.

8. The method according to claim 1, wherein the function comprises a
multiplicative product of a power factor and a temperature factor.

9. The method according to claim 8, wherein the power factor comprises a
difference between the measured power level and a target power level, and
wherein the temperature factor comprises a difference between the
measured temperature and a target temperature.

10. The method according to claim 1, wherein the function is I new =
I present + k Min { ( P targ - P meas P targ )
( T targ - T meas T targ ) } , ##EQU00004## wherein:
Ipresent is a value of current in a previous iteration; Pmeas
is measured power; Ptarg is a target power level; Tmeas is
measured temperature Ttarg is a target temperature; and k is a
damping constant.

11. The method according to claim 1, wherein the function is I new =
I present + kC ( P targ - P meas P targ ) ( T
targ - T meas T targ ) , ##EQU00005## wherein: Ipresent
is a value of current in a previous iteration; Pmeas is measured
power; Ptarg is a target power level; Tmeas is measured
temperature Ttarg is a target temperature; C is a constant having a
value -1 if both Pmeas and Tmeas are greater than Ptarg
and Ttarg, respectively, and +1 otherwise; and k is a damping
constant.

12. The method according to claim 1, wherein controlling the power output
level comprises the steps of: comparing the measured temperature and the
measured power level with a predetermined temperature target value and a
power target value, respectively; and responsively to the step of
comparing varying the power output level to establish a new power output
level so as to approach a predetermined target power value.

13. The method according to claim 12, wherein the step of comparing and
varying the power output level are performed iteratively.

14. The method according to claim 13, wherein the steps of comparing and
varying the power output level are iterated 10 times per second.

15. The method according to claim 13, wherein the steps of comparing and
varying the power output level are iterated 5-50 times per second.

16. The method according to claim 12, wherein the step of varying the
power output level is performed by varying an electrical current
component of the generated energy.

17. The method according to claim 12, wherein the step of varying the
power output level is performed by limiting an increment or decrement
thereof so as not to exceed a predetermined limiting condition, wherein
the limiting condition is selected from the group consisting of a maximum
current, a minimum electrode temperature, a maximum electrode
temperature, a maximum temperature of the tissue, and a maximum power
demand.

18. An ablation apparatus, comprising: a catheter, having a distal
portion for insertion into a body cavity of a living subject and
configured to bring the distal portion into contact with a tissue in the
body cavity; a power generator for generating energy at a power output
level; an ablation electrode disposed on the distal portion, adapted to
accept the energy from the power generator via the catheter and to
conduct the energy to the tissue for ablation thereof; a temperature
sensor disposed on the distal portion for determining a temperature of
the ablation electrode; and a processor operative for determining a
measured temperature of the tissue and a measured power level of the
energy conducted through the ablation electrode for controlling the power
output level responsively to a function of the measured temperature and
the measured power level.

19. The ablation apparatus according to claim 18, wherein the generated
energy is radiofrequency energy.

20. The ablation apparatus according to claim 18, wherein the generated
energy is ultrasound energy.

21. The ablation apparatus according to claim 18, wherein the measured
temperature is an electrode temperature.

22. The ablation apparatus according to claim 18, wherein the generated
energy is laser-produced light energy.

23. The ablation apparatus according to claim 18, wherein the function
comprises a multiplicative product of a power factor and a temperature
factor.

24. The ablation apparatus according to claim 23, wherein the power
factor comprises a difference between the measured power level and a
target power level, and wherein the temperature factor comprises a
difference between the measured temperature and a target temperature.

25. The ablation apparatus according to claim 18, wherein the function is
I new = I present + k Min { ( P targ - P meas
P targ ) ( T targ - T meas T targ ) } ,
##EQU00006## wherein: Ipresent is a value of current in a previous
iteration; Pmeas is measured power; Ptarg is a target power
level; Tmeas is measured temperature Ttarg is a target
temperature; and k is a damping constant.

26. The ablation apparatus according to claim 18, wherein the function is
I new = I present + kC ( P targ - P meas P targ )
( T targ - T meas T targ ) , ##EQU00007## wherein:
Ipresent is a value of current in a previous iteration; Pmeas
is measured power; Ptarg is a target power level; Tmeas is
measured temperature Ttarg is a target temperature; C is a constant
having a value -1 if both Pmeas and Tmeas are greater than
Ptarg and Ttarg, respectively, and +1 otherwise; and k is a
damping constant.

27. The ablation apparatus according to claim 18, wherein the processor
is operative for controlling the power output level by performing the
steps of: comparing the measured temperature and the measured power level
with a predetermined temperature target value and a power target value,
respectively; and responsively to the step of comparing varying the power
output level to establish a new power output level so as to approach a
predetermined target power value.

28. The ablation apparatus according to claim 27, wherein the step of
comparing and varying the power output level are performed iteratively.

29. The ablation apparatus according to claim 28, wherein the steps of
comparing and varying the power output level are iterated 10 times per
second.

30. The ablation apparatus according to claim 28, wherein the steps of
comparing and varying the power output level are iterated 5-50 times per
second.

31. The ablation apparatus according to claim 27, wherein the step of
varying the power output level is performed by varying an electrical
current component of the generated energy.

32. The ablation apparatus according to claim 27, wherein the step of
varying the power output level is performed by limiting an increment or
decrement thereof so as not to exceed a predetermined limiting condition,
wherein the limiting condition is selected from the group consisting of a
maximum current, a minimum electrode temperature, a maximum electrode
temperature, a maximum temperature of the tissue, and a maximum power
demand.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to invasive medical devices. More
particularly, this invention relates to ablation of tissue using such
devices.

[0003] 2. Description of the Related Art

[0004] Ablation of body tissue using electrical energy is known in the
art. The ablation is typically performed by applying alternating
currents, for example radiofrequency energy, to the electrodes, at a
sufficient power to destroy target tissue. Typically, the electrodes are
mounted on the distal tip of a catheter, which is inserted into a
subject. The distal tip may be tracked in a number of different ways
known in the art, for example by measuring magnetic fields generated at
the distal tip by coils external to the subject.

[0005] A known difficulty in the use of radiofrequency energy for cardiac
tissue ablation is controlling local heating of tissue.

[0006] Self-regulating tissue ablators have been proposed to achieve the
desired control. For example, PCT International Publication WO9600036
discusses ablation of body tissue in which ablating energy is conveyed
individually to multiple emitters in a sequence of power pulses. The
temperature of each emitter is periodically sensed and compared to a
desired temperature established for all emitters to generate a signal
individually for each emitter based upon the comparison. The power pulse
to each emitter is individually varied, based upon the signal for that
emitter to maintain the temperatures of all emitters essentially at the
desired temperature during tissue ablation.

[0007] U.S. Patent Application Publication No. 2008/0300588 proposes
performing ablation automatically by monitoring system parameters. When
the ablation is complete, as determined by a processor based on its
reading of the system parameters, RF energy delivery is halted. The
determination is made, preferably without the need for user interaction,
based upon the system parameters and a set of rules for determining
completion. Parameters that may be monitored include power output.

SUMMARY OF THE INVENTION

[0008] There are tradeoffs between the desire to create a sufficiently
large lesion to effectively ablate an abnormal tissue focus, or block an
aberrant conduction pattern, and the undesirable effects of excessive
local heating. If the radiofrequency device creates too small a lesion,
then the medical procedure could be less effective, or could require too
much time. On the other hand, if tissues are heated excessively then
there could be local charring effects due to overheating. Such overheated
areas can develop high impedance, and may form a functional barrier to
the passage of heat. The use of slower heating provides better control of
the ablation, but unduly prolongs the procedure.

[0009] The level of ablator power (P) and the tissue temperature (T) are
key factors in achieving precise control of the delivery of
radiofrequency energy by the catheter electrode. Such control is
important in achieving consistent therapeutic results, while avoiding
excessive injury to surrounding tissues.

[0010] In embodiments of the present invention, radiofrequency (RF)
electrical current applied by an ablator is controlled by feedback based
on the tissue temperature and delivered power. The temperature is
typically measured by a sensor, such as a thermocouple, in the catheter
tip, although other means of temperature measurement may also be used.

[0011] There is provided according to embodiments of the invention a
method of body tissue ablation, which is carried out by inserting a probe
into a body of a living subject, urging the probe into contact with a
tissue in the body, generating energy at a power output level, and
transmitting the generated energy into the tissue via the probe. While
transmitting the generated energy the method is further carried out by
determining a measured temperature of the tissue and a measured power
level of the transmitted energy, and controlling the power output level
responsively to a function of the measured temperature and the measured
power level.

[0012] According to aspects of the method, the generated energy may be
radiofrequency energy, ultrasound energy or laser-produced light energy.

[0013] According to still other aspects of the method, determining a
measured temperature is performed using magnetic resonance imaging
analysis or ultrasound imaging analysis.

[0014] According to an additional aspect of the method, the measured
temperature is an electrode temperature.

[0015] According to one aspect of the method, the function includes a
multiplicative product of a power factor and a temperature factor.

[0016] According to an aspect of the method, the power factor includes a
difference between the measured power level and a target power level, and
wherein the temperature factor includes a difference between the measured
temperature and a target temperature.

[0017] An aspect of the method controlling the power output level includes
iteratively comparing the measured temperature and the measured power
level with a predetermined temperature target value and a power target
value, respectively, and responsively to comparing varying the power
output level to establish a new power output level so as to approach a
predetermined target power value.

[0018] Yet another aspect of the method comparing and varying the power
output level are iterated 10 times per second.

[0019] A further aspect of the method comparing and varying the power
output level are iterated 5-50 times per second.

[0020] In still another aspect of the method varying the power output
level is performed by varying an electrical current component of the
generated energy.

[0021] In an additional aspect of the method varying the power output
level is performed by limiting an increment or decrement thereof so as
not to exceed a predetermined limiting condition, wherein the limiting
condition is selected from the group consisting of a maximum current, a
minimum electrode temperature, a maximum electrode temperature, a maximum
temperature of the tissue, and a maximum power demand.

[0022] There is provided according to embodiments of the invention an
ablation apparatus, including a catheter having a distal portion for
insertion into a body cavity of a living subject and configured to bring
the distal portion into contact with a tissue in the body cavity, a power
generator for generating energy at a power output level, an ablation
electrode disposed on the distal portion, which is adapted to accept the
energy from the power generator via the catheter and to conduct the
energy to the tissue for ablation thereof, a temperature sensor disposed
on the distal portion for determining a temperature of the ablation
electrode. The ablation apparatus further includes a processor operative
for determining a measured temperature of the tissue and a measured power
level of the energy conducted through the ablation electrode for
controlling the power output level responsively to a function of the
measured temperature and the measured power level.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0023] For a better understanding of the present invention, reference is
made to the detailed description of the invention, by way of example,
which is to be read in conjunction with the following drawings, wherein
like elements are given like reference numerals, and wherein:

[0024]FIG. 1 is a pictorial illustration of a system for performing
ablative procedures, which is constructed and operative in accordance
with a disclosed embodiment of the invention;

[0025]FIG. 2 is a schematic illustration of a controller for an ablation
power generator, which is constructed and operative in accordance with a
disclosed embodiment of the invention;

[0026]FIG. 3 is a schematic illustration of a controller for an ablation
power controlled by a temperature sensor based on magnetic resonance
imaging (MRI) analysis, which is constructed and operative in accordance
with an alternate embodiment of the invention; and

[0027]FIG. 4 is a schematic illustration of a controller for an ablation
power controlled by a temperature sensor based on ultrasound analysis,
which is constructed and operative in accordance with an alternate
embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, numerous specific details are set
forth in order to provide a thorough understanding of the various
principles of the present invention. It will be apparent to one skilled
in the art, however, that not all these details are necessarily always
needed for practicing the present invention. In this instance, well-known
circuits, control logic, and the details of computer program instructions
for conventional algorithms and processes have not been shown in detail
in order not to obscure the general concepts unnecessarily.

[0029] Turning now to the drawings, reference is initially made to FIG. 1,
which is a pictorial illustration of a system 10 for performing ablative
procedures on a heart 12 of a living subject or patient, which is
constructed and operative in accordance with a disclosed embodiment of
the invention. The system comprises a catheter 14, which is
percutaneously inserted by an operator 16 through the patient's vascular
system into a chamber or vascular structure of the heart 12. The operator
16, who is typically a physician, brings the catheter's distal tip 18
into contact with the heart wall at an ablation target site. Electrical
activation maps may then be prepared, according to the methods disclosed
in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S.
Pat. No. 6,892,091, whose disclosures are herein incorporated by
reference. Although the embodiment described with respect to FIG. 1 is
concerned primarily with cardiac ablation. The principles of the
invention may be applied, mutatis mutandis, to body tissues other than
the heart. One commercial product embodying elements of the system 10 is
available as the CARTO 3 System, available from Biosense Webster, Inc.,
3333 Diamond Canyon Road, Diamond Bar, Calif. 91765.

[0030] Areas determined to be abnormal, for example by evaluation of the
electrical activation maps, can be ablated by application of thermal
energy, e.g., by passage of radiofrequency electrical current through
wires in the catheter to one or more electrodes at the distal tip 18,
which apply the radiofrequency energy to the myocardium. The energy is
absorbed in the tissue, heating it to a point (typically about 50°
C.) at which it permanently loses its electrical excitability. When
successful, this procedure creates non-conducting lesions in the cardiac
tissue, which disrupt the abnormal electrical pathway causing the
arrhythmia. The principles of the invention can be applied to different
heart chambers, to mapping in sinus rhythm, and when to treat many
different cardiac arrhythmias.

[0031] The catheter 14 typically comprises a handle 20, having suitable
controls on the handle to enable the operator 16 to steer, position and
orient the distal end of the catheter as desired for the ablation. To aid
the operator 16, the distal portion of the catheter 14 contains position
sensors (not shown) that provide signals to a positioning processor 22,
located in a console 24.

[0032] Electrical signals can be conveyed to and from the heart 12 through
one or more electrodes 32 located at or near the distal tip 18 via wires
34 to the console 24. Pacing signals and other control signals may be
conveyed from the console 24 through the wires 34 and the electrodes 32
to the heart 12. Additional wire connections 35 link the console 24 with
body surface electrodes 30 and other components of a positioning
sub-system. The electrodes 32 and the body surface electrodes 30 may be
used to measure tissue impedance measuring at the ablation site as taught
in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein
incorporated by reference. A temperature sensor 37, typically a
thermocouple or thermistor, is mounted on or near each of the electrodes
32.

[0033] The console 24 typically contains one or more ablation power
generator 25. The catheter 14 may be adapted to conduct ablative energy
to the heart using any known ablation technique, e.g., radiofrequency
energy, ultrasound energy, and laser-produced light energy. Such methods
are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924,
and 7,156,816, which are herein incorporated by reference.

[0034] The positioning processor 22 is an element of a positioning
sub-system of the system 10 that measures location and orientation
coordinates of the catheter 14.

[0035] In one embodiment, the positioning sub-system comprises a magnetic
position tracking arrangement that determines the position and
orientation of the catheter 14 by generating magnetic fields in a
predefined working volume its vicinity and sensing these fields at the
catheter using field generating coils 28.

[0036] As noted above, the catheter 14 is coupled to the console 24, which
enables the operator 16 to observe and regulate the functions of the
catheter 14. Console 24 includes a processor, preferably a computer with
appropriate signal processing circuits. The processor is coupled to drive
a monitor 29. The signal processing circuits typically receive, amplify,
filter and digitize signals from the catheter 14, including signals
generated by the above-noted sensors and a plurality of sensing
electrodes (not shown) located distally in the catheter 14. The digitized
signals are received and used by the console 24 and the positioning
sub-system to compute the position and orientation of the catheter 14 and
to analyze the electrical signals from the electrodes.

[0037] Typically, the system 10 includes other elements, which are not
shown in the figures for the sake of simplicity. For example, the system
10 may include an electrocardiogram (ECG) monitor, coupled to receive
signals from one or more body surface electrodes, so as to provide an ECG
synchronization signal to the console 24. As mentioned above, the system
10 typically also includes a reference position sensor, either on an
externally-applied reference patch attached to the exterior of the
subject's body, or on an internally-placed catheter, which is inserted
into the heart 12 maintained in a fixed position relative to the heart
12. Conventional pumps and lines for circulating liquids through the
catheter 14 for cooling the ablation site are provided.

[0038] Reference is now made to FIG. 2, which is a schematic illustration
of a controller 39 for the ablation power generator 25 (FIG. 1), which is
constructed and operative in accordance with a disclosed embodiment of
the invention. The controller 39 comprises a processing unit 41, a memory
43 for storing data and instructions for the processing unit 41, and an
ablation module 45. In some embodiments, instances of the controller 39
may control respective electrodes 32 in a multi-electrode catheter. In
such embodiments the operating parameters and limitations for the power
control algorithm employed in the instances of the controller 39 may be
set globally or independently.

[0039] The ablation module 45 receives temperature signals Tmeas from
each temperature sensor 37 via a respective port 47 and measures
instantaneous power level signals Pmeas from each ablation power
generator 25 via a respective port 49. Only two instances of the
electrodes 32, temperature sensor 37 and the ports 47, 49 are shown in
FIG. 2 for simplicity.

[0040] The function of the controller 39 is to perform ablation while
maintaining a given power output of the ablation power generator 25 as
closely as possible.

[0041] The processing unit 41 determines a deviation between the measured
power level Pmeas and a predetermined target power value; and a
deviation between the measured temperature Tmeas and a predetermined
target temperature. More specifically, the processing unit 41 compares
the temperature signals and the power level signals with preset power
target values Ptarg and temperature target values Ttarg, and
transmits a control signal on line 51 to the ablation module 45, which
controls the ablation power generator 25 so as to produce a new current
value Inew, which is the result of incrementing (or decrementing) an
existing current value Ipresent:

[0044] Power may be measured, for example, using the teachings of commonly
assigned application Ser. No. 12/941,165, filed Nov. 8, 2010, which is
herein incorporated by reference.

[0045] The controller 39 thus increments the current gradually until the
ablator reaches the target power and temperature levels. If either the
power or the temperature (or both) exceeds the target level, the
controller 39 instructs the ablation power generator 25 to reduce the
ablation current in order to avoid injury.

[0046] Typically inputs at ports 47, 49 are read 10 times per second. The
following parameters are read: Voltage (V); Current (I); Temperature (T);
ambient temperature (N). The values Pmeas and Tmeas and the
impedance Zmeas are computed from the general formulas:

P=V*I;

Z=V/I.

[0047] The impedance values are displayed for the operator and used to
confirm continuity in the system.

[0060] Initially, power demand is typically set at 250 units
(corresponding to about 1 W) using a digital-to-analog converter, but can
be increased up to 2048 units. In subsequent iterations, changes in power
demand are can be calculated as follows:

ΔD=D0*Min((Pt-Pmeas)/Pt,(Tt-Tmeas)/(-
Tt)) Eq. (4).

where D0 is a constant predefined change in the demand or power (250
units in the demand around 1 W of power). At each iteration, the current
value (I) corresponding to the power

Di+1=Di+ΔD Eq. (5)

is output onto the electrode.

[0061] However, if Min ((Pt-Pmeas)/Pt,
(Tt-Tmeas)/(Tt))>1, the equation

ΔD=D0 Eq. (6)

is used, in order to limit the increment in the power level. If

Min((Pt-Pmeas)/Pt,(Tt-Tmeas)/(Tt))<-1.1-
,

then the power output is set at 0 in order to allow the tissue to cool.

[0062] The iteration rate for the algorithm is typically 10/sec, but can
be in the range of 5-50/sec.

[0063] If the current power is more than required, i.e.,
Pt<Pmeas or Tt<Tmeas, then the value ΔD
is negative and the power output will be decreased. Power is increased
only when the current power is lower than desired and none of the above
restrictions are exceeded.

[0064] In some cases ablation may continue when one or more of the
above-noted limitations are violated, but in a restricted mode of
operation. The following example is illustrative: [0065] 1. If the
power required (Demand) exceeds available power (MaxDemand) or the
electrode temperature exceeds its maximum, ablation may continue in
restricted mode at suboptimum power.

[0066] In other cases, ablation is terminated, as illustrated by the
following examples: [0067] 2. An abrupt change in impedance that
exceeds a limiting value signifies a potentially hazardous condition,
e.g., a surface skin patch may be become disconnected. [0068] 3.
Exceeding the maximum temperature limit, which can be caused by failure
of a cooling pump. [0069] 4. Failing to exceed the minimum temperature.
This is a safeguard, intended to prevent inadvertent ablation of tissues
other than the target tissue. Violation of this threshold causes the
ablation to terminate [0070] 5. Power output exceeding Pt may
indicate a short circuit. [0071] 6. Elapsed ablation time has exceeded a
maximum limit. Although ablation terminates in this event, this is done
for operational reasons, and not because of hardware failure. [0072] 7.
Violating the minimum flow rate. This may indicate pump failure. The flow
rate is typically tested functionally at the beginning of a procedure,
before energizing the ablation power generator 25 (FIG. 2). An electrode
temperature reduction of 1-3° C. is expected when the pump is
energized.

Alternate Embodiment 1

[0073] Reference is now made to FIG. 3, which is a schematic illustration
of the controller 39 for the ablation power generator 25 (FIG. 1), which
is constructed and operative in accordance with an alternate embodiment
of the invention. In this embodiment the temperature sensors 37 (FIG. 2)
may be omitted, which reduces manufacturing costs. Indication of the
tissue temperature can be obtained by concurrently performing magnetic
resonance imaging (MRI), directed at the target tissue. Dependencies of
T1, T2, and proton density on temperature are used to relate change in
signal strength to temperature.

[0074] MRI signals from field magnets 53 are acquired by a reconstruction
processor 55, which is enhanced by a peak calculation module 57 that is
linked to a temperature analyzer 59. The temperature analyzer 59 provides
a thermometry signal to the port 47 of the ablation module 45. Thus, the
MRI system operates as a temperature sensor for purpose of ablation
control. Thermometry techniques presented, e.g., on the Internet at
"wiki.medpedia.com/Clinical:Focused_ultrasound_ablation_offer
prostate_cancer_option" can be used mutatis mutandis in this embodiment.

Alternate Embodiment 2

[0075] Reference is now made to FIG. 4, which is a schematic illustration
of the controller 39 for the ablation power generator 25 (FIG. 1), which
is constructed and operative in accordance with yet another alternate
embodiment of the invention. In this embodiment the temperature sensors
37 (FIG. 2) may be omitted. Tissue temperature are measured by assessing
thickness of the tissues being ablated, using the teachings described in
commonly assigned U.S. application Ser. No. 11/357,512, entitled "Lesion
Assessment by Pacing", which is hereby incorporated by reference.

[0076] An array of ultrasound transducers 61 is placed generally near the
distal tip 18 of the catheter 14 (FIG. 1), and are energized by an
ultrasound driver 63. One example of a suitable ultrasound driver that
can be used for this purpose is an AN2300® ultrasound system produced
by Analogic Corporation, Centennial Drive, Peabody, Mass. Ultrasound
driver 63 may support different imaging modes such as B-mode, M-mode, CW
Doppler and color flow Doppler, as are known in the art.

[0077] Signals from the transducers 61 are received in an ultrasound
processor 65, and further analyzed in a temperature analyzer 67. The
temperature analyzer 67 provides a thermometry signal to the port 47 of
the ablation module 45. A sub-system comprising the ultrasound components
described in this embodiment functions as a temperature sensor for
purposes of ablation control.

Alternate Embodiment 3

[0078] The energy sources in the previous embodiments produce RF energy.
However, the invention can be carried out using other energy types. For
example, in the embodiment of FIG. 4, the electrodes 32 (FIG. 2) can be
omitted, and the transducers 61 configured to emit higher levels of
ultrasound energy as taught in commonly assigned U.S. Pat. No. 7,156,816,
which is herein incorporated by reference.

[0079] Alternatively, the source of ablative energy may be a laser, as
disclosed in commonly assigned U.S. Pat. No. 6,997,924, which is herein
incorporated by reference.

[0080] In either case temperature may be measured using any of the
embodiments disclosed above.

[0081] It will be appreciated by persons skilled in the art that the
present invention is not limited to what has been particularly shown and
described hereinabove. Rather, the scope of the present invention
includes both combinations and sub-combinations of the various features
described hereinabove, as well as variations and modifications thereof
that are not in the prior art, which would occur to persons skilled in
the art upon reading the foregoing description.